The present invention is directed toward a friction rock stabilizer and, more particularly, toward a friction rock stabilizer that includes an improved point anchor for increased holding strength and life expectancy.
Ground support, especially in the mining industry, is an important safety factor that must be taken into consideration during any type of excavating activity. Rock stabilizers, or rock bolts, have been used for many years to support exposed rock during mining operations. A number of types of rock bolts are used depending on the situation, such as ground conditions, costs, personal preferences, etc. There are three primary types of rock bolts. The first is an expansion shell type bolt where a screw threaded steel bar is inserted into a drilled hole in the rock. The bolt has a “shell” at its tip. Once the bolt is inserted into the drilled hole and is turned, the shell expands to the sides of the hole and grips the rock so that the steel bar can then be tensioned. This results in bolting the rock strata layers together.
Grouted bar type stabilizers are also known. These include a ribbed bar which is inserted into a drilled hole and which hole is then further filled with a specialized cement or resin-based grout. This type of support depends directly on the bond between the rock and the grout and the grout and the steel bar and acts like a reinforcing bar.
Another effective anchoring system that is currently used is commonly referred to as a Split Set available from International Rollforms of Deptford, N.J. A Split Set is a brand of a friction rock stabilizer that includes an elongated tube and a bearing plate. The tube is typically made from resilient steel and has a slit along its length so that the tube will be compressible for insertion into a pre-drilled bore in a mine roof or wall. One end of the tube is tapered and the other end has a ring flange. In order to install the split set, the bearing plate is placed against a surface to be supported, such as a wall or roof of a mine. The tapered end of the tube is then driven through the aperture and as the tube slides into place, the slot narrows. The tube exerts radial pressure against the surface over its full contact length and provides plate load support. The result is a tight grip brought about by the friction generated between the outer steel wall of the tube or cylinder and the inner side wall of the bore in the wall. Such systems are described, for example, in U.S. Pat. No. 5,295,768 to Buchhorn et al., U.S. Pat. No. 4,652,178 to Kates et al., U.S. Pat. No. 4,445,808 to Arya, and U.S. Pat. No. 4,382,719 to Scott.
The interior of these rock stabilizers can frequently corrode due to the steel being exposed to the atmosphere within the mine. Over time, this can limit the useful life of the stabilizer. It has been known, therefore, to fill the interior of the cylindrical rock stabilizer after it has been inserted into the bore with a grouting material. This helps not only to improve the useful life of the stabilizer but also to increase its holding strength.
Even further, and as described more fully in published PCT Application No. WO 99/05031 to Smith, it is also known to crimp the tube or form indentations or undulations at various places along the length of the stabilizer and which communicate with the open slit. These indentations allow the grout or other resinous material to extrude out of the interior of the stabilizer, through the slit and into the recessed area or undulation formed in the outer wall of the stabilizer. This allows more of the grout to come in contact with the bore hole and to increase the frictional holding of the stabilizer. The grout also helps to insulate the outer wall of the stabilizer from moisture to thereby increase the longevity thereof.
It is also known to utilize wedges within the rock stabilizer to increase the frictional holding thereof. This is accomplished by forcing a wedge-shaped member into the interior of the stabilizer after the stabilizer has been driven into place so that it can engage a portion of the interior wall of the stabilizer or another wedge-shaped member therein to expand a portion of the stabilizer wall to force it into contact with the interior wall of the bore. Examples of such devices are described in U.S. Pat. No. 4,312,605 to Fu et al., U.S. Pat. No. 4,098,087 to Swain, and published PCT Application No. WO 88/02437 to Hilton.
While the above-described systems are individually well known and the wedge expanders of the prior art may be of some use, the wedge expanders are somewhat complex and difficult to employ in the field.